President Trump tweeted Sunday that he “would be willing to shut down government” at the end of September if Congress doesn’t get serious about border security.

In the tweet—and in a follow-up tweet Monday—the president renewed his call for faster funding of a border wall but curiously made no mention of another border security measure that arguably would be as effective as the wall at curbing illegal immigration.

That would be mandating the use by all employers of E-Verify, the federal database to confirm that their workers are in the country legally.

Trump called for the E-Verify mandate in a campaign stump speech two years ago in August 2016, but it since seems to have fallen down the memory hole.

If jobs are the magnet that attracts illegal immigrants to and across the southern border, it follows that to “demagnetize” illegal immigration will require eliminating, or at least dramatically reducing, the lure of employment here.

But in the reporting on the debate in Congress in late June on immigration-reform legislation, there was virtually no mention of E-Verify, which likely would do at least as much to curtail illegal border-crossing as Trump’s proposed “big, beautiful wall.”

(That’s not to suggest that the two are mutually exclusive. To the contrary, together they would be doubly effective.)

The tougher of the two immigration bills that Congress debated and voted on last month did include the requirement that all employers utilize the federal E-Verify database.

It went down to defeat 193-to-231 on June 21, however, with 41 centrist Republicans joining all 190 Democrats who voted in opposition.

That made it clear that neither open-borders liberals who crave more than anything else a “path to citizenship” for undocumented future Democratic voters nor the Main Street Partnership-style moderate Republicans who carry water for the Chamber of Cheap Labor are serious about addressing the problem of illegal immigration.

Coincidentally, that vote came just a day after federal immigration-enforcement personnel arrested 146 workers in a raid at a meatpacking plant in Salem, Ohio. U.S. Immigration and Customs Enforcement said Fresh Mark might have knowingly hired illegal immigrants, many of whom were fraudulently using identifications of U.S. citizens.

Democrats and those centrist Republicans unwilling to get serious about stopping illegal immigration need to be made to explain why they are OK with this widespread form of ID theft, which is a felony under the federal Identity Theft and Assumption Deterrence Act of 1998. That 20-year-old law carries with it penalties of up to 15 years in prison and a maximum fine of $250,000.

According to the National Conference of State Legislatures, 20 states require the use of E-Verify by at least some public and/or private employers. The other 30 should, too, which is why a nationwide federal mandate is necessary.

But because of a jobless rate at a 17-year low, and concomitant labor shortages in the agriculture, construction and hospitality industries, The Washington Post reported, the enactment of a federal E-Verify mandate “remains in limbo.”

It has been since at least January 2012.

When the topic of immigration reform came up then at a Republican presidential debate, former Massachusetts Gov. Mitt Romney said that “self-deportation” would go a long way toward stemming the tide of illegal immigrants in the country.

In response to a question at the debate in Tampa, Florida, the GOP nominee-to-be said it wouldn’t be necessary to “round people up” and deport them, because they would leave of their own accord—out of financial necessity—because they wouldn’t be able to get jobs in the U.S.

“The answer is self-deportation, which is, people decide they can do better by going home because they can’t find work here, because they don’t have legal documentation to allow them to work here,” Mr. Romney said.

“We’d have a card that indicates who’s here illegally,” he explained. “And if people are not able to have a card, and have through an E-Verify system determine that they are here illegally, then they’re going to find they can’t get work here.

“And if people don’t get work here, they’re going to self-deport to a place where they can get work,” he said.

Four years later, another Republican presidential candidate threw his support behind E-Verify, a database administered by U.S. Citizenship and Immigration Services.

“We will ensure that E-Verify is used to the fullest extent possible under existing law,” Trump said in an August 2016 campaign speech in Phoenix, in the border state of Arizona, “and we will work with Congress to strengthen and expand its use across the country.”

Fully 79 percent of respondents favored requiring employers to use E-Verify to ensure that all new hires are in the country legally, according to an ABC News-Washington Post poll last September.

The poll’s findings came two weeks after a September report by the Federal Reserve Bank of Dallas showed the efficacy of E-Verify in five states where it’s required of most employers.

“The key takeaways from this study are that E-Verify, when it’s mandatory and all employers have to use it, can have very large deterrent effects on the employment of undocumented immigrants and possibly also on the immigration of undocumented immigrants, or illegal immigration,” said Dallas Fed Vice President Pia Orrenius.

Apologists for illegal immigration on both sides of the aisle contend that illegal aliens do the jobs Americans won’t, but that suggests they’re OK with the illegal immigrants being exploited in low-wage employment.

If E-Verify were enacted by Congress and mandated nationwide, squeezing out the labor of illegals, Econ 101 tells us, market forces would drive up wages to where Americans would take those heretofore unappealing jobs.

One would think that that would be reason enough for unions and Democrats who push for increases in the minimum wage to support E-Verify.

A beefed-up agricultural guest-worker program could address any remaining labor shortages after the enactment of E-Verify. But low-priced fruits and vegetables are not sufficient reason not to require it.

Trump should make good on his 2016 campaign promise and push Congress to make E-Verify the law of the land.

Peter Parisi is a freelance writer-editor based in Northern Virginia. He was a writer and editor for The Washington Times for 17 years.

The views and opinions expressed in this commentary are those of the author and do not reflect the official position of The Daily Caller.